Craft a Work Bench
Craft a Furnace
Craft an Anvil
Mine Iron Ore or Lead Ore
Smelt the ore into Iron Bars or Lead Bars
Chop wood from trees
Open the Work Bench crafting menu
Craft 10 Wood
Craft 2 Iron Bars or 2 Lead Bars
Craft 1 Chain from 1 Iron Bar or 1 Lead Bar
Craft the Sawmill at the Work Bench using 10 Wood, 2 Iron Bars or 2 Lead Bars, and 1 Chain